During conventional semiconductor integrated circuit manufacturing (e.g., during VLSI manufacturing), it is occasionally necessary to modify a logic circuit design within the integrated circuit. It is therefore a common conventional practice to provide some spare logic gates, such as inverters, AND gates, NOR gates, etc., which can hopefully be used to make the desired modifications in the logic circuit design. Unfortunately, there is no way to insure that these spare gates will provide the particular logic functionality that is required to implement the desired change in the logic circuit design. For example, the spare gate may be a NAND gate, when the desired change in the logic circuit design calls for the insertion of a NOR gate.
Even if a spare logic gate is available to provide the logic functionality required by the desired change in the logic circuit design, the process of inserting the spare logic gate into the logic circuit design typically requires changing the photolithographic masks associated with at least one metal layer and one via layer of the integrated circuit. Modification of a photolithographic mask can be a relatively expensive operation in the integrated circuit manufacturing process.